In general, a brake system is used to decelerate, stop, or park a moving vehicle.
Among brake systems, an electronic mechanical brake (EMB) system, which uses an electronically controlled motor as a power source in order to generate a braking force, generates a braking force without using hydraulic pressure. Therefore, the electronic mechanical brake system has a simpler structure as compared to a hydraulic pressure brake. Further, the electronic mechanical brake system comes into the spotlight as a brake system that can optimally implement various electronic devices and an integrated chassis.
During the braking, self-energizing of a wedge assembly operated by an actuator is performed in the electronic wedge brake (EWB) that is an example of the electronic mechanical brake (EMB) system. That is, a wedge is moved due to the drive of the actuator and presses the pad and a frictional force between the pad and the wheel disk serves as an additional input force. Due to the above-mentioned wedge operation, it is possible to obtain a large braking force for the performance of the motor.
In addition, the EWB can implement various additional functions, such as a function for maintaining a set clearance of a pad, a wheel lock prevention (or referred to as Fail-Safe) function for suppressing a brake failure to prevent a vehicle from being abnormally rotated during normal driving, and an EPB (Electronic Parking Brake) function.
The present applicant has filed several applications about the above-mentioned EWB to the Korean Intellectual Property Office. For example, the following brake system has been disclosed in Korean Patent Application No. 10-2007-0065114. The brake system implements a main braking function with power generated by one motor. Further, the brake system implements various additional functions, such as a function for maintaining a set clearance of a pad, a wheel lock prevention function, and an EPB (electronic parking brake) function, by using a NSL (Non-Self Locking) screw and a solenoid mechanism interlocked with a main braking motor.
However, if one motor is used as a main power source and a solenoid and a NSL (Non-Self Locking) screw are used as described above, an excessive load is applied to some components when a main braking function and various additional functions are implemented. For this reason, there is a problem in that the durability of the components may deteriorate.
In particular, the above-mentioned excessive load is applied during the implementing of an EPB (electronic parking brake) function. The EPB function requires a force, which is relatively smaller compared to the main braking function but is large. That is, when park braking is performed, a park braking force is maintained while the solenoid is turned off. Accordingly, it is difficult to constrain an axial reaction force transmitted from a pad by only using a NSL (Non-Self Locking) screw.
Therefore, there is a problem in that it is a little difficult to maintain a park braking force during park braking.